Congestive heart failure results from the inability of the heart to pump blood throughout the body at its normal pace, causing blood to flow a slower rate with increased pressure. As a result, the heart is unable to meet the oxygen and nutrient demands of an individual's vital organs. Heart failure may be caused by cardiomyopathy, heart valves damage, coronary heart disease, hypertension, and, in some cases, diabetes. Worldwide, more than a million patients currently suffer from congestive heart failure. In the United States alone, thousands of patients with congestive heart failure are candidates for heart transplantation or an electro-mechanical heart implant, such as a ventricular assist device.
Ventricular assist devices (VAD) are implantable electro-mechanical pumps that are used to partially or completely replace the function of a failing heart. Ventricular assist devices do not replace the heart entirely, but rather assist the right (RVAD) or left (LVAD) ventricle in their ability to pump blood. The choice of the device depends on the underlying heart disease and the pulmonary arterial resistances, which determines the load on the right ventricle. LVADs are more common, as RVADS are typically only necessary when pulmonary arterial resistance is very high.
VADs require a power source to operate the pump. Typically, the VAD is connected to an external power source by a transcutaneous drive line. The exit site of the drive line from the abdomen provides a portal of entry for pathogens, making VAD recipients highly vulnerable to device-related infections. However infectious complications are not limited to VAD systems, as infections are common in many medical devices that use transcutaneous power line.
As an alternative to the transcutaneous power lines, wireless power transfer systems were developed to deliver power to implanted medical devices, including VADs. The traditional approach is TET (transcutaneous energy transfer), in which the energy source is directed toward the energy harvesting device with the goal to minimize RF exposure of the patient. In one commercial embodiment, the receiver coils are located under the patient's skin and the transmitter above the skin. Such TET systems are very sensitive to misalignment and movement of the implanted coil. Additionally, the coil implanted in a separate surgical procedure. Another shortcoming of the current TET solution is that the electromagnetic field density is so high that it can cause heating of the skin and even burns. That is, when the receiver is receiving energy, regular resistance losses within the coil can cause heating to the same volume of tissue receiving the electromagnetic radiation and add heating to it. When the transmitter attached to the receiver is transmitting energy, regular resistance losses within the transmitter coil can cause heating that adds to the receiver regular resistance losses heating and to the receiving electromagnetic radiation heating. The accumulated heat can become a complex issue. TET systems have also suffered setbacks due to complexity and lack of efficiency.